Screw-thread-cutting device



March 17, 1931. w. c. JOHNSON SCREW THREADCUTTING DEVICE Filed Aug. 15, 1927 a7 3 F y 4 INVENTOR.

Patented Mar. 17, 1931 WILLIAM C. JOHNSON, OF MILWAUKEE, WISCONSIN SCREW-THR-EAD-GUTTING DEVICE Application filed August 13, 1927. Serial No. 212,816.

Figure 1 is a view in vertical central section on the line 11 of Fig. 3.

Figure 2 is a view on the line 2-2 of Fig. 3.

Figure 3 is a view on the line and looking in the direction of 33 of Fig. 2 and Fig. 4.

Figure 4 is a view on the line 4t of Fig. 3.

Figure 5 is a detached perspective view of one of the cutter guides.

Figure 6 is a detached perspective view of one of the cutters.

My invention relates to an improved screw thread cutting device of the type employing a plurality of cutters mounted in inclined positions in a holder, the object being to produce a simple efiicient device having few parts with little machining, to have a bearing surface over the cutting edge, to wedge the cutters firmly in place while threading, to project the ends of the cutters beyond the holder for threading close to a shoulder, to provide for long life of the cutters by having thread cutting teeth at both ends, to partially enclose the cutters for safety purposes when the device is rotating, to provide for simplicity in cutter construction, to provide for simple and efiicient adjustment of the cut ters, to minimize the movement of parts, for operation in more economy of space.

The device shown consists of a plurality of cutters 1 mounted in inclined positions in the holder 2, the cutters having thread cutting teeth 3 at both ends, a keyway 5 in the side 6' of said cutters at right angles to the axis of the device and a key 7 in the cutter guide 8 directly engaging the said keyway, an enclosing member 9 having a conical bore 10 and held firmly against the conical bearing surface of the holder 2, said enclosing member having a plurality of bearing surfaces 12 directly in sliding engagement with the outer inclined bearing surfaces 13 of said cutters. The circumferential lip 14 of the said enclosing member extends over the circumferential lip 15 of the sleeve 16, partially enclosing the cutters. The cutter guides 8 are held firmly in the mating member 19, pass through and into the slots 17, of the holder 2, said holder having sliding engagement thereon and also having sliding engagement on the large trunuionl the small trunnion 1.1 of the mating member. The plunger 18 is forced inwardly by longitudinally sliding the sleeve 16 which has an angular bearing surface in the bore thereof and directly engaging the angular bearing surface 20 located at the outer end of the plunger. Adjacent to the angular bearing surface 20 of the plunger is a step 21, and when the plunger is suificiently forced inwardly the part of the said plunger adjacent to the said step will be removed from its position against the surface of the conical bore 32 of the adjusting screw 22 the expand ing action of the springs 23 will then move the holder 2 and the enclosing member 9 longitudinally forward only so far as the length of the said step permits; and the adjusting screw, being mounted in the holder, will move with the said holder until part of the conical bore 32 of the adjusting screw strikes the surface 37 of the said plunger the cutters in their respective slots will simultaneously move outwardly on a plane at right angles to the axis of the device while said holder moves forward and the cutter guides 8 and the mat ing member 19 remain stationary.

To simultaneously move the cutters inwardly at right angles to the axis of the device, 1 reverse the movement of the sleeve 16, said sleeve having pins 24 mountedin the inner face 25 thereof and abutting the inner ends 26 of the pawls 27, said pawls having sliding engagement in the recesses 36 of the mating member 19 and pivotally mounted on pins 28 in the said mating member, said pins passing through the pawls 27, the outer ends 29 of the pawls directly engaging recesses 30 located in the rear of holder 2, said outer ends abutting the surfaces 35 of the recesses 30, the sliding action of the said sleeve causing the pawls 27 to pivot on the pins 28 in their respective recesses, thus moving the holder to its initial position, compressing the springs 23 and allowing the plunger 18 to snap into place against the angular bearing surface of the sleeve 16, the expansion of the spring 34 forcing the plunger outward. The cutter guides 8 remain stationary while the cutters are simultaneously moved, inwardly toward each other as described.

The simple construction of the adjusting screw 22 provides for precision adjustment of the cutters inwardly or outwardly, the adjusting screw having spirally cut threads 31 on its periphery matching with spirally cut threads in the holder, said adjusting screw having a conical bore 32 the axis of which is at an angle to the axis of the device, the angular position of the said adjusting screw bringing aart of the surface of the conical bore 32 in line with the plunger 18 and in direct contact with a part of the periphery thereof. The operation of the adjusting screw 22 is best made when the plun er 18 has been forced inwardly and the border 2 moves forward aspreviously described; the sleeve 16 can then be moved rearwar-dly sufliciently to allow one to turn the said adjusting screw inwardly or outwardly, thus changing slightly the position of that portion of the surface of the conical bore which is at right angles to the axis of the device; said sleeve is then moved forward and the plunger snaps in place again, bringing the portion of the plunger adjacent to the step, in line with the surface of the conical bore as described.

The device is provided with a shank 38 to be inserted into the grip of a machine so adapted for the use of a device of this sort, and when the rotating rod to be threaded is moved into the device and threads out thereon in the usual manner, a stop on the machine will move the sleeve in the direction of the shank, and the sleeve with its angular bearing surface will move the plunger from its initial locking position to its final locking position against the plunger, the holder is then allowed to move forward simultaneously moving the cutters outwardly so that the cutting threads on the cutters clear the rod, thus limiting the length of the threading operation. To retract the cutters for the next threading operation the sleeve is moved forward toward the cutters by means attached to the machine, and the pin in the sleeve abutting the pawls pivotally mounted in the mating member actuates the pawl, said pawls having their outer ends movable in the recesses of the holder. The lever action of the pawls moves the holder rearward toward the shank sufliciently to allow the plunger to move into its initial locking position in the adjusting screw and simultaneously moving the cutters on a plane at right angles to-the axis of the device to their initial cutting position.

I am aware of the fact that it is old to cut screw threads with a device having cutters open away from the threads when the cutting is completed, to close inwardly for the initial insertion of the blank to be threaded and to provide for the adjustment of the cutters, but, I do claim to have new and useful improvements embodied in my invention for obtaining the results so stated.

lVhat I claim is In a screw thread cutting device, a mating member provided with a shank, a holder slid able longitudinally on the mating member, cutter guides mounted in the mating member in parallelism with the axis and passing through said holder, thread cutters mounted in slots in the holder at an acute angle to the axis of the device, two of the ends of each of the cutters being adapted to cut threads, a keyway in the side of each of the cutters at right angles to the axis of the device while the cutters are in the inclined position, said keyway being centralized between the cutting ends of the cutters for reversal purposes in their respective slots and being operative in the device while in either position, a key at the end of each of the cutter guides and entering the guideway of a cutter whereby the cutters are slidable on the keys in their slots in the holder inwardly or outwardly on a plane at right angles to the axis of the device through the longitudinal rearward or forward movement of the holder on the mating member.

In testimony whereof, I have signed this specification.

lVILLIAM C. JOHNSON. 

